<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .container{
            background:red;
            width:200px;
            height:200px;
            margin: 100px;

            /* 外阴影 */
            /* box-shadow: 5px 5px 10px 0 rgba(0,0,0,.2); */

            /* 下面是内阴影 */
            /* box-shadow: inset 5px 5px 10px 0 rgba(0,0,0,.2); */


            box-shadow: 0 0 0 5px green;
        }
    </style>
</head>
<body>
    <div class="container">
    </div>
</body>
</html>
